all Python 3OOPfunction

__getitem__

magic methods

The method behind indexing: obj[k] calls obj.__getitem__(k). A slice arrives as a slice object.

Syntax

def __getitem__(self, key): ...

A __getitem__ with integer indexes is enough to make an object iterable: for walks 0, 1, 2… until IndexError. Mappings conventionally raise KeyError and sequences IndexError — dict.get and iteration rely on that difference. obj[1:3] passes slice(1, 3, None).

Examples

class Squares:
    def __getitem__(self, i):
        if i >= 5:
            raise IndexError(i)
        return i * i
s = Squares()
print(s[3])  # → 9
print(list(s))  # → [0, 1, 4, 9, 16] — итерация через __getitem__

class Show:
    def __getitem__(self, key):
        return key
print(Show()[1:3])  # → slice(1, 3, None)

See also

Common errors

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